single ended or differential input

what is the difference between these configurations on an ADC ?

Reply to
Tareq Matar
Loading thread data ...

uh, ...throw away half the capability?

Reply to
RobertMacy

First answer was flippant, so....

Balanced has some attributes that can really improve dynamic range and performance. Plus, many parts support 'balanced' operation. The main one for me is that a balanced system will almost ALWAYS have a lower noise floor. Envision two conductors in a shield that each go a mirrored voltage away from each other. Difficult to inject noise there. Now envision a receiver that looks at two incoming conductors again with balanced voltages on them, again difficult to misunderstand the signal.

In other words, the signal going down a blanaced connection is 'self contained' and does NOT rely on anything else.

Single ended, well. you have now included a 'common' connection that has a lot of other signals using it!

Does that explain some of the advantage?

Also, in single ended as you try to use that common connection, as you go up in frequency, parasitic components [all those components you usually ignore like series inductance and leakage cpacitances] start to rear their ugly heads and you have little hope of everything working well, so balanced is the ONLY way to go.

Reply to
RobertMacy

Two input wires versus one!

For slow ADCs, like delta-sigmas, diff can eliminate ground-loop errors.

Fast pipeline ADCs seem to have less distortion if they are used in differential-input mode; has something to do with the internal charge-based digitizer stages.

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

Thing is, you don't really need it on the ADC. tha tis local, with local co mmons. Where differential really helps in in the transmission of the signal s. Like LVDS. That is how the signal gets to your TV in some cases.

It seems actually easier to achieve a high CMRR with lower levels, so they chose the levels for like HDMI cables and all that because of that. You don 't need forty volts of video.

Even wiht LVDS they usually shield the transmission cables becae you CAN sw amp theinput amps with noise in common mode, and there is a limit. But when you get to a CMRR of lik 200:1, you're doing pretty good. shiled that nad it is gojng to be pretty much noise free.

One of the reasons for low voltage in a LVDS system also is that the wires have capacitance. Too much voltage swing requires better slew rates in the amps both feeding and recieving the signal. This costs money. So this is a compromise now, use a lower signal level and you don't need to pour as much money in the amps for a given bandwidth. with a lower bandwidth you might choose a higher signal level and be sloppier with the physical wiring, mayb e even do without any shieldiong as long as you don't bother the FCC.

Reply to
jurb6006

Actually, balanced helps a great deal on the ADC. Input voltage noise limits the ADC's noise floor. Single eneded means the signal can go from

+rail through GND to -rail. a 2 rail range. Now consider a balanced system where one side goes from +rail through GND to -rail and the other side goes opposite from -rail through GND to +rail, signal range of 4 rails! Thus you gain 6dB.

And sorry I snipped too much, but *if* you do balance correctly, you'll breeze through FCC Compliance requirements WITHOUT shielding your cables. Actually run 100Mbs over a carefully made twisted pairof wires, no shielding. However, single ended can be a strain at high frequencies, where a shielded coax can 'leak' like a sieve and fail compliance.

Consider single ended stripline in a PCB structure. Even in a six, or 8, layer PCB using 1/2 oz copper the shielding you get between striplines can be irritatingly low, [from memory] 106dB down which is usually ok, but not great if it's important.

Done properly, the same PCB stackup using balanced can get better than

138dB shielding, [again from memory] but I do remember better than 30dB improvement adjacent and over 60dB improvement in further out layers.
Reply to
RobertMacy

--
A single-ended input will connect one of the inputs to ground, while 
a differential input will let both inputs float and evaluate the 
 Click to see the full signature
Reply to
John Fields

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.